The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 41 334.7, filed on Aug. 31, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1 . Field of the Invention
The invention relates to a machine for producing and/or treating a material web, in particular a paper or cardboard web, having at least one heatable unit, such as in particular a pressing roll, a drying cylinder, and/or the like, which is wrapped around part of its outer cylindrical surface by the material web and at least one wire and an outer sealing belt, and having an overpressure cap that subjects the heatable unit to a liquid or gaseous medium under pressure.
2. Discussion of Background Information
It is known to dry material webs on cylinders, between two steel belts (U.S. Pat. No. 4,461,095) or between a heated cylinder and a steel belt or sealing belt (DE 197 23 163 A1). A drying section of the type mentioned initially is described in DE 197 23 163 A1.
While no sealing is necessary in the case of drying on one cylinder, it is necessary in the case of drying between a heated cylinder and an externally cooled steel belt or sealing belt to prevent the cooling medium from entering the dry space between the steel belt or sealing belt. Specifically, a steam pressure should arise between the heated cylinder and the paper that drives the as yet unvaporized water from the paper to the cooled side of the paper in the wires. Also in the case of drying between two steel belts, the space in which the paper and the wires are located, and also the space for the cooling and heating medium, must be sealed. Here, sealing of the paper space is usually accomplished by a lateral thickening of the wires in the form of a sealing bead. The space for the cooling and heating medium is closed off by costly seals such as, in particular, flat surfaces with high speeds relative to the steel belts traveling along with the paper web.
The present invention provides a machine of the type initially mentioned in which, in the simplest possible manner, the region occupied by the material web and the at least one wire or felt is reliably sealed with respect to the pressure chamber of the overpressure cap, on the one hand, and this pressure chamber is reliably sealed with respect to the outside, on the other hand.
The invention includes a sealing belt that is wider than the material web and the wire, such that both of its lateral edge regions extend past them. Further, both of its edge regions are pressed so as to seal against the surface of the heatable unit by the overpressure prevailing in the pressure chamber of the overpressure cap. Additionally, or alternatively, the pressure chamber of the overpressure cap can be sealed with respect to the outside at each of its two end faces by a seal that is located between an end wall of the stationary overpressure cap and an opposing wall, in particular a radial, cylinder-side opposing wall.
On the basis of this design, an extremely reliable seal of the region occupied by the material web and the at least one wire, and/or of the pressure chamber of the overpressure cap, is achieved with minimal cost in a simple manner. An underpressure can be created or maintained with the relevant seal of the region occupied by the material web and the wire, which results in an increase in drying performance. Moreover, entry of the liquid or gaseous medium is prevented. Because of the appropriate sealing of the pressure chamber of the overpressure cap, a structural pressure can be applied which results not only in greater drying performance, but also in improved paper characteristics.
The liquid or gaseous medium under pressure can be, in particular, a cooling medium. As a result of the fact that the temperature of the liquid or gaseous medium is lower than the temperature at the outer side of the part of the outer cylindrical surface of the heatable element wrapped by the material web and the wire, a high degree of liquid removal from the material web can be achieved. One or more wires can be provided, where it is possible in such a case that a wire located further outside has a coarser structure than a wire located further inside. In the case of several wires, they can be separate from one another or they can be connected together at least partially. The sealing belt can be separate, or connected to at least one wire belt.
At least one cylinder-side opposing wall is preferably located in the vicinity of an end of the heatable element.
In one useful practical embodiment, the material web and the wire are arranged in a recess provided on the outer cylindrical surface of the heatable unit with the sealing belt being wider than this recess and both of the lateral edge regions of the belt extending beyond it. The depth of the recess can be at least essentially the same as the overall height of the material web and wire.
It is also advantageous for the opposing edges or side walls of the recess to be coated with a material that is heat resistant, flexible, and seals well, for example such as Teflon, silicone, or the like. In this way, sealing the space between the heatable unit and the material web is significantly improved, and the steam pressure produced in this space during drying is increased. Accordingly, the quantity of water expelled from the material web is also increased, and the drying performance is improved for the same heat output.
For an even more reliable seal of the region occupied by the material web and the wire, it is useful to provide at least one sealing pocket or chamber opposite each lateral edge region of the sealing belt and covered thereby. It is advantageous for at least one sealing pocket or chamber to be located opposite each of the two lateral edge regions of the sealing belt. In certain cases, it can be useful for at least two sealing pockets or chambers to be located opposite at least one of the two edge regions of the sealing belt.
In a preferred embodiment, at least one sealing pocket or chamber is provided that is connected to the surroundings and accordingly is under ambient or atmospheric pressure. As a result of the defined pressure difference between the relevant sealing chamber and the pressure chamber of the overpressure cap, sufficient contact force on the sealing surface can be ensured. If coolant fluid enters a sealing pocket or chamber as a result of a failure, this fluid is carried away by the relevant connecting channel(s), bore(s), or passageway(s), which can serve as an indicator of leakage.
More usefully, the at least one cylinder-side opposing wall can be formed by a disk arranged at the relevant end of the heatable unit. In this context, the sealing force can be applied, for example, by the preloading of the overpressure cap as a result of the internal pressure, or it can be applied mechanically. When the sealing force is generated by the internal pressure, the overpressure cap is pressed against the disk and the seal is automatically subjected to a preloading corresponding to the pressure. When the internal pressure changes, the preloading of the seal adjusts automatically.
In another advantageous embodiment, at least one cylinder-side opposing wall is formed by a shoulder provided in the vicinity of each bearing journal of the heatable unit, and the relevant end face of the overpressure cap is extended to the region of this bearing journal. For example, the seal can be located in the vicinity of the bearing journal or at some point in the middle. In this case as well, the sealing force can again be applied by the preloading of the cap as a result of the internal pressure, or mechanically. As a result of the fact that the relevant opposing wall and the seal are located in the vicinity of the bearing journal, the relative speed between the rotating and the stationary part is lower, which reduces wear on the seal accordingly.
It is advantageous for at least one end face of the heatable unit to be provided with a heat-resistant material, which reduces to a minimum the direct flow of heat between the heatable unit and the cold coolant.
In certain cases, it is useful for at least one seal located between an end face of the stationary overpressure cap and a cylinder-side opposing wall to be acted upon by a resilient element arranged between the end face and the opposing wall. In particular, this may be a mechanical element with at least one spring, for example.
Of course, the pressure chamber of the overpressure cap can also be sealed with respect to the outside by at least one non-contacting seal, such as a labyrinth seal or the like.
The heatable unit can, for example, also be provided as a shoe-press replacement with a very long nip.
According to an aspect of the present invention an apparatus for at least one of producing and treating a material web is provided having at least one wire; an outer sealing belt, which is wider than the at least one wire, comprising a pair of lateral edge regions; at least one heatable unit, having an outer cylindrical surface, wherein the at least one wire and the outer sealing belt are at least partially wrapped around the at least one heatable unit; an overpressure cap arranged to form a pressure chamber containing a medium under pressure, the medium under pressure exerting a pressure on the at least one heatable unit; and at least one of: (a) a seal formed between the lateral edge regions and the heatable unit; and (b) a seal formed between end faces of the overpressure cap and an opposing wall to seal the pressure chamber from an external environment.
According to another aspect of the present invention, the at least one heatable unit includes at least one of a pressing roll and a drying cylinder. Additionally, other aspects of the present invention includes an opposing wall which is a radially extending opposing wall.
In another aspect of the present invention, the opposing wall includes an axial end face of the at least one heatable unit. According to a further aspect of the present invention the opposing wall radially extends from a bearing journal. In another aspect of the present invention the opposing wall radially extends from an axial end region of said at least one heatable unit.
According to still a further aspect of the present invention the at least one heatable unit includes a recessed area having a width less than a width of the sealing belt. Further aspects of the invention include wherein the lateral edge regions of the sealing belt are arranged axially outside of the recessed area. According to other aspects of the present invention the at least one wire is positioned within said recess.
According to another aspect of the present invention, the material web includes at least one of paper and cardboard web. According to a further aspect of the present invention the depth of the recess is at least approximately the same as the overall height of the material web and wire. According to a still further aspect of the invention, the recess is defined by two opposing edge walls on the outer cylindrical surface of the at least one heatable unit.
According to an aspect of the present invention, the opposing edge walls of the recess are coated with a material that is heat resistant, flexible, and a sealant. According to another aspect of the present invention, the material is one of TEFLON and silicone.
Additionally, other aspects of the present invention include at least one sealing pocket or chamber provided on the outer cylindrical surface of the at least one heatable unit, and located opposite each lateral edge region of the sealing belt and covered thereby.
In another aspect of the present invention, at least two sealing pockets or chambers are provided on the outer cylindrical surface of the at least one heatable unit, and located opposite at least one of the two lateral edge regions of the sealing belt. According to a further aspect of the present invention, at least one sealing pocket or chamber is provided that is connected, by at least one of a channel, bore, and passageway, to ambient or atmospheric pressure.
In another aspect of the present invention, at least one end face of the at least one heatable unit is provided with a heat-resistant material. According to a further aspect of the present invention, the pressure chamber is sealed with respect to the outside by at least one non-contacting seal.
In another aspect of the present invention, at least one heatable unit is provided as a shoe-press replacement. According to a still further aspect of the present invention, the at least one wire includes a plurality of wires wherein a wire located further outside has a coarser structure than a wire located further inside. Further aspects of the invention include a resilient element that is positioned between the opposing wall and end face of said overpressure cap, wherein the seal is acted upon by the resilient element.
According to other aspects of the invention, the resilient element includes a mechanical element with at least one spring. According to another aspect of the invention, the opposing wall is a radial cylinder-side opposing wall attached to an end of the at least one heatable unit. According to a further aspect of the present invention at least one cylinder-side opposing wall is formed by a disk arranged at an end of the at least one heatable unit.
According to another aspect of the invention, the at least one seal is located between an end face of the cap and a cylinder-side opposing wall, and is acted upon by a resilient element arranged between the end face and the opposing wall. Additionally, other aspects pf the present invention include wherein the resilient element includes a mechanical element with at least one spring.
In another aspect of the invention, a process for producing and treating a material web, is provided including partially wrapping a material web around at least one heatable unit using at least one wire; pressurizing, with a medium, a pressure chamber positioned around at least a portion of the at least one heatable unit, whereby the medium exerts pressure on the at least heatable unit; sealing the material web and at least one wire between the at least one heatable unit and an outer sealing belt; and rotating the at least one heatable unit to process the material web.
According to a further aspect of the invention, a heat transfer effect occurs from the at least heatable unit toward the sealing belt. According to a still further aspect of the present invention, the process further includes relieving a pressure, buildup between the sealing belt and the at least one heatable unit to an external atmosphere using at least one of a channel, bore, and passageway.
In another aspect of the present invention, the process further includes removing a fluid buildup between the sealing belt and the at least one heatable unit to an external atmosphere using at least one of a channel, bore, and passageway. Further aspects of the invention includes wherein the pressurized medium exerts pressure on lateral edge portions of the outer sealing belt against the at least one heatable unit.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.